The present invention relates to a flow control system for controlling a flow of a medium passing through a pipe part of a pipe system via which the medium is distributed from a common source to a plurality of consumer devices, according to the preamble of claim 1.
In residential, and in particular in non-residential buildings, several applications are known which make use of a pipe system that distributes a medium from a common source to a number of consumer devices spread over the building. Such a pipe system may be a closed circuit, comprising a number of supply pipes connecting the common source with each of the consumer devices and a number of return pipes connecting each of the consumer devices back to the common source. This is for instance the case where the consumer devices are heat exchange systems. The pipe system may also be an open circuit, comprising a number of supply pipes connecting the common source with each of the consumer devices only, without return pipes connecting each of the consumer devices back to the common source. This is for instance the case in sanitary applications. Such a pipe system may also be a combination of a closed circuit and an open circuit. This is for instance the case when heating water is delivered from a common source to a number of heat exchangers, which are provided to heat up the rooms in the building, and to a number of water taps, which are provided to deliver heated water to the consumer.
In such systems it is known to include control valves with an adjustable orifice for controlling the flow of medium to the respective consumer device. The position of the orifice determines the amount of medium passing through the consumer device per time unit. In heat exchange applications this means that the position of the orifice determines the amount of heat delivered from the heat exchanger to the room. However, the amount of medium passing through the consumer device is not only determined by the position of the orifice, but also by the pressure at which the medium is passed through the consumer device as well as by other influencing factors. This pressure differs depending on for example the distance between the common source and the consumer device. This is in particular the case in non-residential buildings, where the pipe system and the consumer devices are in most cases divided over a plurality of different floors in the building. The pressure at a specific consumer device may even vary over time, for instance as a result of closing or opening a valve in a pipe to one or more other consumer devices. In heat exchange applications, the closing of such a valve may lead to an increase of the pressure of the medium flowing to one or more of the other heat exchangers in the circuit and hence to a higher flow rate towards these heat exchangers and to an increase of the amount of energy/heat delivered by the heat exchangers to the respective room. This is not desired.
Several systems were already developed to attempt to provide in a pressure independent control of the medium flow through a pipe system.
WO-A-9206422 is for instance related to a system for automatically adjusting the medium flow to a set medium flow, independent of pressure variations between the entrance and exit of the heat exchanger. To this end the control system comprises a first medium flow control unit, set to a predetermined value, and a second medium flow control unit, that allows to create a variable pressure loss. The control system further comprises a mechanic drive mechanism for automatically compensating each detected variation of pressure loss between the entrance and exit of the heat exchanger by more or less closing the second flow medium flow control unit. The pressure difference between entrance and exit, and thus the set medium flow, is only set once. The control system has the disadvantage that only minor medium flow variations can be compensated, restricting the applicability range of the system.
Another type of control system for pipe systems is known from U.S. Pat. No. 6,435,207. U.S. Pat. No. 6,435,207 describes a flow regulation control valve for setting and measuring volume flows in pipes. The flow regulation control valve comprises a shut-off member arranged in a flow chamber, for setting a desired flow state and a sensor arranged in or adjacent the flow chamber, for sensing a value representative of a flow through the flow chamber. The flow regulation control valve further comprises an evaluation unit which determines the flow from the value measured by the sensor and from the characteristic values of the section control valve which are stored in an electronic data store at the sensor. These characteristic values are valve specific. The adjustment of the flow through a section of the pipe system is done by manually adjusting the shut-off member of the flow regulation control valve until the desired flow is displayed in the evaluation unit. Such a control system has the disadvantage that the characteristic values of the housing are used to determine the actual flow rate. The characteristic values or characteristic curve of a control valve gives the correct relationship between the medium flow and the position of the control valve only at constant pressure. The system can be calibrated for use at a given nominal pressure, as a result of requiring the characteristic values of the control valve, only a narrow range of pressure variations can be accurately compensated for.
U.S. Pat. No. 5,927,400 discloses a flow control system for controlling flow to a heat exchanger. The system comprises a turbine type flow sensor in which a turbine is driven by the flowing medium. The number of revolutions per time unit of the turbine is counted to measure the flow rate of the medium at the turbine. The sensor outputs a pulse signal created by magnets on the turbine, so the number of pulses per time unit is a measure for the flow rate. An evaluation unit, using preset characteristics depending on the flow range, compares the measured flow rate with a set flow rate, which is derived from a temperature setting, and operates a valve accordingly. The system has the disadvantage that its accuracy is poor, especially at low flow rates, again restricting the applicability range of the system.